Ultra-high Energy Cosmic Ray Physics Research Articles

Measurement of the average very forward energy as a function of the track multiplicity at central pseudorapidities in proton-proton collisions at sqrt{s}=13,text {TeV}

The average total energy as well as its hadronic and electromagnetic components are measured with the CMS detector at pseudorapidities -6.6<eta <-5.2 in proton-proton collisions at a centre-of-mass energy sqrt{s}=13,text {TeV} . The results are presented as a function of the charged particle multiplicity in the region |eta |<2. This measurement is sensitive to correlations induced by the underlying event structure over a very wide pseudorapidity region. The predictions of Monte Carlo event generators commonly used in collider experiments and ultra-high energy cosmic ray physics are compared to the data. All generators considered overestimate the fraction of energy going into hadrons.

Constraining QCD transport coefficients in hadron colliders

We review the phenomenology of relativistic nuclear collisions in the light of ultra-high energy cosmic ray physics. A novel phase of quantum chromodynamics called quark-gluon plasma is expected to appear in nuclear collisions at high energies. The produced hot matter is found to be well-described as a relativistic fluid with small viscosity. We show that the transport coefficient can be quantitatively extracted by comparing theoretical estimations of viscous hydrodynamic models to experimental data.

The current status of research in ultrahigh-energy cosmic ray physics: A brief review

The origin and nature of ultrahigh-energy cosmic rays (UHECRs, E > 1018 eV) is one of the most intriguing unsolved problems of modern astrophysics. This review is dedicated to the current status of research in this field. We describe the largest ongoing experiments carried out at the Pierre Auger Observatory and Telescope Array, at the first orbital detector of UHECRs, that is, TUS, and for the KLPVE and JEM-EUSO orbital telescopes, which are currently being developed. We discuss the latest results on the energy spectrum and mass composition of UHECRs and the relationship between UHECRs on the one hand and ultrahigh-energy neutrinos and photons on the other. Finally, we review the latest results on the anisotropy of the arrival directions of UHECRs, which is a crucially important area of research in the search for astrophysical sources of cosmic rays in the highest energy range.

Ultra-high energy cosmic rays: Setting the stage

The history of ultra-high energy cosmic ray physics is reviewed from the post-war era of arrays such as Volcano Ranch, Haverah Park and Akeno to the development of air-fluorescence and current hybrid arrays. The aim of this paper is to present the background information needed for a better understanding of the current issues in this field that are discussed in much greater depth in the rest of this conference. a. Pre-history: the discovery of cosmic radiation and the study of its penetrating power. This led to great debates between Millikan and Compton about the kinds of particles that composed it. The discovery of the latitude effect followed by the East-West effect conclusively proved that the majority of the cosmic ray particles were positively charged (protons and nuclei). b. Ancient history: the discovery that high energy cosmic radiation produced extensive air showers and that much of the cosmic radiation on the surface was the result of secondary processes in the atmosphere. This was also the era when the presence of very high energy particles in the primary radiation was clearly demonstrated (by B. Rossi, P. Auger and others). c. Middle Ages: the post-war development of large area surface detectors covering areas up to 10km 2 coming from the pioneering work of B. Rossi., J. Linsley and others. d. Renaissance: the development of fully calorimetric techniques based on air-fluorescence (by the Fly's Eye group, based on earlier work of J. Keuffel, K. Greisen and others) and the extension of ground arrays to 100km 2 (AGASA). e. Modern times: the refinement of air-fluorescence techniques (HiRes) and the construction of hybrid air-fluorescence/surface array detectors of unprecedented scale (Pierre Auger Observatory (PAO), Telescope Array (TA)). 2. POST-WAR DEVELOPMENTS

A BAYESIAN APPROACH TO COMPARING COSMIC RAY ENERGY SPECTRA

A common problem in ultra-high energy cosmic ray physics is the comparison of energy spectra. The question is whether the spectra from two experiments or two regions of the sky agree within their statistical and systematic uncertainties. We develop a method to directly compare energy spectra for ultra-high energy cosmic rays from two different regions of the sky in the same experiment without reliance on agreement with a theoretical model of the energy spectra. The consistency between the two spectra is expressed in terms of a Bayes factor, defined here as the ratio of the likelihood of the two-parent source hypothesis to the likelihood of the one-parent source hypothesis. Unlike other methods, for example chi^2 tests, the Bayes factor allows for the calculation of the posterior odds ratio and correctly accounts for non-Gaussian uncertainties. The latter is particularly important at the highest energies, where the number of events is very small.

Constraints from the first LHC data on hadronic event generators for ultra-high energy cosmic-ray physics

The determination of the primary energy and mass of ultra-high-energy cosmic-rays (UHECR) generating extensive air-showers in the Earth’s atmosphere, relies on the detailed modeling of hadronic multiparticle production at center-of-mass (c.m.) collision energies up to two orders of magnitude higher than those studied at particle colliders. The first Large Hadron Collider (LHC) data have extended by more than a factor of three the c.m. energies in which we have direct proton–proton measurements available to compare to hadronic models. In this work we compare LHC results on inclusive particle production at energies s = 0.9 , 2.36 , and 7 TeV to predictions of various hadronic Monte Carlo (MC) models used commonly in cosmic-ray (CR) physics ( qgsjet, epos and sibyll). As a benchmark with a standard collider physics model we also show pythia (and phojet) predictions with various parameter settings. While reasonable overall agreement is found for some of the MC, none of them reproduces consistently the s evolution of all the observables. We discuss implications of the new LHC data for the description of cosmic-ray interactions at the highest energies.

Cosmic ray threshold in an asymptotically de Sitter spacetime

We discuss the threshold anomaly in ultrahigh energy cosmic ray physics by assuming that the matter world just be a perturbation of a de Sitter universe, which is consistent with the recent astronomical observations: about two-thirds of the whole energy in the Universe is contributed by a small positive cosmological constant. One-particle states are presented explicitly. It is noticed that the dispersion relation of free particles is dependent on the degrees of freedom of angular momentum. This fact can be regarded as the effects of the cosmological constant on kinematics of particles.